Energy absorber



United States Patent ENERGY ABSORBER Curtis M. Hepperle, Cedar Rapids,Iowa, assignor to Co!- Radio Company, Cedar Rapids, Iowa, a corporation0 owa Application March 3, 1950, Serial No. 147,500

3 Claims. (Cl. 343-18) This invention relates in general to energyabsorbers, and in particular to a high frequency broad-bandnonreflecting attenuator.

It is often desirable in testing antennas and transmitters to terminatein a non-reflective load. One method of obtaining such a termination isto point the antenna toward open space so that none of the energy whichis transmitted will be reflected. At times this becomes inconvenient inthat the radiating antenna must always be placed in the open, and attimes even the transmitter must be placed outside. In radiometry it isusually necessary to calibrate the receiver by directing the antennatoward a non-reflecting surface of known temperature.

It is an object of this invention, therefore, to provide means forterminating an antenna in a manner so that it may be tested inside abuilding.

A further object is to provide a broad band non-reflecting absorber formagnetic waves which will substantially absorb all of the impingingenergy.

Yet another object is to provide a non-reflective energy absorber to beused as a calibration device for a radiometry receiver.

A feature of this invention is found in the provision for a supportingframe adapted to hold a plurality of lossy strips spaced laterally apartin a position so as to intercept electromagnetic waves.

Further objects, features, and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which:

Figure l is a front isometric view of the energy absorber of thisinvention; and,

Figure 2 is a sectional view taken on a line 22 of Figure 1.

Referring to Figure 1, a frame of dielectric material such as woodcomprises the upper and lower members 11 and 12, respectively, and theside members 13 and 14. A plurality of lossy sheets or strips 16 of awidth L substantially equal to the width of the frame 10 are supportedbetween the members 11 and 12 parallel to the side walls 13 and 14. Thestrips 16 are spaced equidistant apart, as shown in Figure 2.

The material is lossy and may be, for example, coarse fabric strips. TheUnited States Rubber Company manufactures a cloth named Uskon which maybe used, for example. As used herein, the term lossy is an adjectivewhich indicates that the loss in a material is appreciable when comparedto incident energy. See second paragraph, page 274, Fields and Waves inModern Radio, Ramo and Whinnery, published by John Wiley 1944. The endsof the strips 16 are attached to the end walls 11 and 12 by gluing orother suitable holding means. If the distance between each of the lossystrips 16 is designated as d, electromagnetic waves impinging on thefront of the energy absorber will be shorted and attenuated if the wavelength of the energy is greater than the d dimension and less than 2d.In other words, the attenuator is broad band in that it attenuates overa range of wave lengths from d to 2d. Thus no tuning is required withinthis range, as is necessary in the conventional type of 2,724,112Patented Nov. 15, 1955 energy absorbers which comprise a flat piece oflossy material supported in front of a metal sheet, with the distancebetween them being A wave length. It is seen in this instance that theattenuator must be tuned, in that the A wave length distance will changefor each frequency. The broad band characteristic of the presentinvention is a major improvement over this type of energy absorber.Another advantage, which is a corollary of the above one, is that thedimension d need not be maintained to a very small tolerance.

The dimension L of the strip 16 affects the attenuating characteristicof the energy absorber. Another variable is the type of material used inthe strips, and if the resistivity of the material is 377 ohms persquare, optimum performance is obtained. If any energy passes throughthe attenuator and is reflected through it from the reverse direction,it will be decreased again as it passes through it from the reversedirection, and should be negligible when it arrives at the transmitteronce again. The lossy strips might be mounted on the four walls and roofof a room to obtain a space room from which no reflection will beforthcoming between the wave length from d to 2d.

It is seen that this invention provides means for terminating an antennain a non-reflecting manner over a relatively broad band of frequencies,and thus makes it possible to calibrate antennas and radiometricreceivers within the confines of a building.

Although this invention has been described with respect to a particularembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope as defined by the appended claims.

I claim:

1. An electromagnetic wave attenuator comprising a frame member definingan axially extending opening, and a plurality of laterally disposed,equally spaced lossy strips of electrically conductive material havingthe impedance of free space extending across said opening, each stripsupported at each end by said frame member parallel to the remainingstrips.

2. A broad band non-reflecting absorber for electromagnetic wavescomprising, a frame member, a plurality of laterally disposed lossystrips extending across said frame member with each strip parallel tothe remaining strips, the lateral distance between eachstripsubstantially constant and the distance between strips being greaterthan one-half wave length of the energy to be absorbed and less than onewave length of the energy to be absorbed.

3. A broad band non-refiecting absorber of electromagnetic radiantenergy comprising, a frame member, a plurality of electrically resistivestrips of cloth having the impedance of free space, each of said stripsbeing supported by said frame member with the broad sides of the stripsparallel and laterally spaced apart between the limits of a half wavelength and one Wave length of the energy to be absorbed.

References Cited in the file of this patent UNITED STATES PATENTS2,461,005 Southworth Feb. 8, 1949 2,464,006 Tiley Mar. 8, 1949 2,464,269Smith Mar. 15, 1949 2,474,384 Sunstein June 28, 1949 2,491,662 HoughtonDec. 20, 1949 2,508,479 Wheeler May 23, 1950 2,526,573 Mason Oct. 17,1950 2,527,918 Collard Oct. 31, 1950 2,538,035 Pickles Jan. 16, 19512,588,249 Kock Mar. 4, 1952 FOREIGN PATENTS 802,728 France June 13, 1936

